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Abstract:

A reflection-type display device (200) with a plurality of pixel regions
(40) includes: alight modulation layer (1); a front substrate (10) and a
rear substrate (12) between which the light modulation layer (1) is held;
electrode structures (18 and 56) for varying optical characteristics of
the light modulation layer (1) for each pixel region (40); a
retroreflective layer (2) which is placed on a rear side of the light
modulation layer (1); and a non-retroreflection member (53) which is
placed on the rear side of the light modulation layer (1) and which has
reflection characteristics different from retroreflection. The front
substrate (10) includes alight shielding layer (20) which defines an
opening (50) in the each pixel region (40), and the opening contains a
non-retroreflection region (50n), which is defined by the
non-retroreflection member (53), and a retroreflection region (50r),
which is defined by the retroreflective layer (2).

Claims:

1. A reflection-type display device with a plurality of pixel regions,
comprising:a light modulation layer;a front substrate and a rear
substrate between which the light modulation layer is held;an electrode
structure for varying optical characteristics of the light modulation
layer for each pixel region;a retroreflective layer which is placed on a
rear side of the light modulation layer; anda non-retroreflection member
which is placed on the rear side of the light modulation layer and which
has reflection characteristics different from retroreflection,wherein the
front substrate comprises a light shielding layer which defines an
opening in the each pixel region, andwherein the opening contains a
non-retroreflection region, which is defined by the non-retroreflection
member, and a retroreflection region, which is defined by the
retroreflective layer.

2. The reflection type display device according to claim 1, wherein, when
viewed from a normal line direction of the rear substrate, the
non-retroreflection region takes up 1/3 or less of an entire area of the
opening.

3. The reflection-type display device according to claim 1, wherein the
non-retroreflection region is disposed at a rim of the opening.

4. The reflection-type display device according to claim 1, wherein the
retroreflective layer is placed across the rear substrate from the light
modulation layer.

5. The reflection-type display device according to claim 4, wherein the
non-retroreflection member is interposed between the retroreflective
layer and the light modulation layer to reflect part of light entering
the retroreflective layer from a viewer side in a direction different
from a retroreflection direction.

6. The reflection-type display device according to claim 1, further
comprising wiring lines which are formed on the rear substrate,wherein
part of the wiring lines is placed within the opening to function as the
non-retroreflection member.

7. The reflection-type display device according to claim 1,wherein the
electrode structure comprises:a counter electrode, which is formed on the
front substrate; andpixel electrodes, which are formed on the rear
substrate and spaced apart from one another for the each pixel
region,wherein the pixel electrodes each comprise:a reflective metal
layer; anda transparent conductive layer, andwherein at least part of the
reflective metal layer is placed within the opening to function as the
non-retroreflection member.

8. The reflection-type display device according to claim 1,wherein the
electrode structure comprises:a counter electrode, which is formed on the
front substrate; andpixel electrodes, which are formed on the rear
substrate and spaced apart from one another for the each pixel
region,wherein the reflection-type display device further comprises a
reflective metal layer, which is placed between the pixel electrodes and
the retroreflective layer, andwherein at least part of the reflective
metal layer is placed within the opening to function as the
non-retroreflection member.

9. The reflection-type display device according to claim 7, wherein the
wiring lines formed on the rear substrate are shielded against light by
the light shielding layer and the reflective metal layer.

10. The reflection-type display device according to claim 1, wherein the
non-retroreflection member comprises a substantially flat
non-retroreflection region.

11. The reflection-type display device according to claim 10, wherein the
non-retroreflection region is parallel to the rear substrate.

12. A reflection-type display device with a plurality of pixel regions,
comprising:a light modulation layer;a front substrate and a rear
substrate between which the light modulation layer is held;an electrode
structure for varying optical characteristics of the light modulation
layer for each pixel region; anda retroreflective layer which is placed
between the rear substrate and the light modulation layer, and which has
a plurality of unit features arranged two-dimensionally,wherein the front
substrate comprises a light shielding layer which defines an opening in
the each pixel region, wherein the retroreflective layer comprises a
plurality of reflection electrodes, which are spaced apart from one
another for the each pixel region,wherein the reflection-type display
device further comprises:a plurality of switching elements which are
formed on the rear substrate; anda contact portion which electrically
connects each of the reflection electrodes with its associated switching
element,wherein the plurality of reflection electrodes each comprise,
within the opening:a retroreflection region, which includes the plurality
of unit features; anda substantially flat non-retroreflection region,
andwherein the non-retroreflection region is placed above the contact
portion and, when viewed from a normal line direction of the rear
substrate, is larger in area than each unit feature.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a reflection-type display device
and its manufacturing method.

BACKGROUND ART

[0002]Reflection-type display devices that operate in a scattering display
mode with the use of a retroreflection plate have been proposed. In the
scattering display mode, a change in voltage applied to a light
modulation layer such as a liquid crystal layer allows the light
modulation layer to switch between a transmitting state in which light is
transmitted and a scattering state in which light is scattered, and the
display device utilizes this to display an image or the like. A display
device using this display mode does not need a polarizing plate and may
therefore have an enhanced light utilization efficiency. Another
advantage resides in that the viewing angle dependence is small. The
structure of this type of display device is disclosed in, for example,
Patent Documents 1 to 4.

[0003]The operation principle of the above-mentioned reflection-type
display device is described below with reference to FIGS. 1(a) and 1(b).
FIGS. 1(a) and 1(b) are diagrams illustrating display device's "black"
displaying state and "white" displaying state, respectively. The "white
displaying state" here refers to a display state in which the liquid
crystal layer is in the scattering state. Accordingly, in the case of
color display, the highest gray scale in gray scale display is called a
"white displaying state" irrespective of what color is displayed. The
"black displaying state," on the other hand, refers to a display state in
which the liquid crystal layer is in the transmitting state, and
indicates the lowest gray scale in gray scale display.

[0004]As illustrated in FIG. 1(a), when a light modulation layer (here,
scattering-type liquid crystal layer) 1 is controlled to keep the
transmitting state, what a viewer 6 sees is the retroreflection plate
itself. Incident light 3 from a light source 5, which is outside the
display device, passes through the light modulation layer 1 and then
reflected by a retroreflection plate 2 toward a direction in which the
light has entered (reflected light 4b). Light from the light source 5
therefore does not enter the eyes of the viewer 6, and the "black"
displaying state is obtained.

[0005]When the light modulation layer 1 is controlled to keep the
scattering state, the incident light 3 from the light source 5 is
scattered by the light modulation layer 1 as illustrated in FIG. 1(b). In
the case where the light modulation layer 1 is a forward scattering-type
liquid crystal layer, most of the incident light 3 is scattered forward
by the light modulation layer 1, reflected by the retroreflection plate
2, and then exits to the side of the viewer 6 through the light
modulation layer 1 in the scattering state (reflected light 4w).
Scattering by the light modulation layer 1 nullifies the retroreflection
of the retroreflection plate 2, thereby preventing the incident light 3
from traveling back to the incident direction. Part of the incident light
3 is scattered backward by the light modulation layer 1 and exits to the
side of the viewer 6 (not shown). The display device in this case is in
the "white" displaying state because part of the light that has exited to
the side of the viewer 6 reaches the eyes of the viewer 6. According to
this operation principle, the forward scattering as well as backward
scattering of the light modulation layer 1 may be utilized effectively,
and the obtained "white" display is therefore brighter.

[0006]The retroreflection plate 2 illustrated in FIG. 1 may be a layer
that has retroreflection characteristics (retroreflective layer) Corner
cube arrays, microsphere arrays, microlens arrays, and other arrays in
which unit components (corner cubes, microspheres, or the like) are
arranged two-dimensionally may be employed.

[0007]A corner cube array is an array of two-dimensionally-arranged corner
cubes each of which is constituted by three faces orthogonal to one
another. Light incident on a corner cube is, ideally, reflected by three
faces that constitute this corner cube to return to the same direction as
the incident direction. The use of a corner cube array which may have a
high retroreflection rate improves the display contrast ratio of a
reflection-type display device. Patent Document 3 describes that the
display contrast ratio of a reflection-type display device employing a
corner cube array is enhanced further by using a corner cube array that
is made up of minute corner cubes as a retroreflection plate. A corner
cube array made up of minute corner cubes (arrangement pitch: 5 mm or
less, for example) is called herein as a micro corner cube array
"(MCCA)".

[0008]The structure of a reflection-type display device that uses an MCCA
as a retroreflection plate is described next.

[0009]A reflection-type display device using an MCCA may have, for
example, a structure in which the MCCA is placed across a display panel
from the viewer. A structure like this where the MCCA is placed outside
of the display panel (hereinafter referred to as "external MCCA
structure") is disclosed in, for example, Patent Document 4. A "display
panel" herein refers to a panel structured such that a light modulation
layer such as a liquid crystal layer and voltage application means for
applying a voltage to the light modulation layer are formed between two
opposing substrates. Of the two opposing substrates, a substrate that is
on the viewer side is called a "front substrate" and a substrate on the
opposite side from the viewer is called a "rear substrate". In an
external MCCA structure, the MCCA is placed on the rear side of the rear
substrate.

[0010]Reflection-type display devices having a structure in which the MCCA
is placed between the two substrates of the display panel (hereinafter
referred to as "internal MCCA structure") have also been proposed. For
instance, the aforementioned Patent Document 3 describes a structure in
which the retroreflective layer is placed between the modulation layer
and the rear substrate in the display panel.

[0011]A concrete description is given below with reference to drawings on
the conventional structure of a reflection-type display device having a
retroreflection plate (retroreflection-type display device). The
description takes as an example a reflection-type liquid crystal display
device that has an external MCCA structure.

[0012]FIG. 2(a) is a plan view illustrating a state of wiring lines and
electrodes on the rear substrate of the conventional retroreflection-type
liquid crystal display device. FIG. 2(b) is a diagram illustrating the
structure of the conventional retroreflection-type liquid crystal display
device, which is a schematic cross-sectional view taken along lines
II-II' and II'-II'' in the plan view of FIG. 2(a).

[0013]A display device 100 includes a front substrate 10 and a rear
substrate 12 disposed so as to be opposed to the front substrate 10.
Between the substrates 10 and 12, a light modulation layer (here,
scattering-type liquid crystal layer) X which is capable of taking a
scattering state or a transmitting state is provided. A retroreflective
layer 2 is provided on a side of the rear substrate 12 that is opposite
from the light modulation layer 1.

[0014]Formed on the same side of the rear substrate 12 as the light
modulation layer 1 are a plurality of thin film transistors (TFTs) 13,
which function as switching elements, source lines 14, gate lines 15 for
selectively driving the thin film transistors 13, and others. A plurality
of pixel electrodes 16 are placed above the thin film transistors 13, the
source lines 14, and the gate lines 15, with a transparent resin layer 22
in-between. These pixel electrodes 16 each define a pixel, which
constitutes one unit of displaying an image. Each pixel electrode 16 is
electrically connected to a drain electrode 13d of its associated thin
film transistor 13 through a contact portion 24 provided in the
transparent resin layer 22.

[0015]The pixel electrodes 16 are formed by using an electrically
conductive material which transmits light, e.g., indium tin oxide (ITO)
As illustrated in FIG. 2(b), the pixel electrodes 16 are disposed so as
to be spaced apart, thus defining pixels, each of which is one unit of
image displaying. On the other hand, generally, wiring lines such as the
source lines 14 and the gate lines 15 are formed by using a metal
material, e.g., tantalum. Though not illustrated, the wiring lines 14 and
15 are respectively connected to a source driver and a gate driver in a
driving circuit which is provided on the rear substrate 12.

[0016]On the front substrate 10, a counter electrode 18 including color
fitters 19, a black matrix 20, and a transparent conductive film is
provided. The color filters 19 are provided for the respective pixels.
The black matrix 20 is disposed between adjoining pixels and in the
neighborhood of the display region so as to shield the wiring lines 14
and 15 and the thin film transistor 13 against light. Typically, the
width of the black matrix 20 is set sufficiently larger than the width of
each source line 14 (d>0), or substantially equal to the width of each
source line 14 (d=0).

[0017]In the display device 100, by controlling the voltage which is
applied between the counter electrode 18 and the pixel electrode 16, it
becomes possible to switch the light modulation layer 1 between a
scattering state and a transmitting state in each pixel.

[0018][Patent Document 1] JP 05107538 A

[0019][Patent Document 2] JP 2000-19490 A

[0020][Patent Document 3] JP 2002-107519 A

[0021][Patent Document 4] JP 11-15415 A

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

[0022]The inventors of the present invention has found out through a study
a problem with the retroreflection-type display device 100 exemplified in
FIGS. 2(a) and 2(b) in that, when the light modulation layer 1 is in the
scattering state (i.e., white displaying state), the displayed image is
not bright enough in some viewing directions.

[0023]The above-mentioned problem is described in more detail with
reference to drawings.

[0024]First, FIG. 3(a) is referred to. In the white displaying state,
light incident on the display device 100 from the light source 5 passes
through the light modulation layer 1 before reflected back to a direction
30 of the light source 5 ("retroreflection direction") by the
retroreflective layer 2. The light is then scattered again by the light
modulation layer 1 and exits to the viewer side. Scattered light La which
exits to the viewer side after scattered by the light modulation layer 1
in this manner has an angle distribution centered around the
retroreflection direction 30 as schematically illustrated in the drawing.
Accordingly, when the retroreflection direction 30 and the viewing
direction of the viewer 6 are relatively close so that part of the
scattered light La which is denoted by Lo exits in the viewing direction
as illustrated in the drawing, the light Lo contributes to the brightness
of the displayed image.

[0025]Referring to FIG. 3(b), a contrasting case is examined in which the
exit direction of the scattered light La is significantly distant from
the viewing direction of the viewer 6. As illustrated in the drawing,
when the viewing direction and the retroreflection direction (i.e.,
direction of the light source 5) 30 are far from each other with respect
to the normal line direction of the substrates 10 and 12, the light La
scattered by the light modulation layer 1 does not have sufficient
intensity in the viewing direction, with the result that the displayed
image is not bright enough.

[0026]This problem could be lessened by enhancing the scattering power of
the light modulation layer 1. However, enhancing the scattering of the
light modulation layer 1 increases the proportion of light that is
trapped as a result of total reflection by the surface of the front
substrate 10, namely, light that does not exit to the viewer side due to
a refractive index difference at the interface between the display panel
and the air, to the light La scattered by the light modulation layer 1.
This lowers the light utilization efficiency. In addition, enhancing the
scattering power of a scattering-type liquid crystal layer used as the
light modulation layer 1 generally raises the drive voltage.

[0027]Conventional retroreflection-type display devices thus have a
problem in that the displayed image is not bright and is low in
visibility depending on the direction in which a viewer views the display
panel.

[0028]The present invention has been made in view of the above-mentioned
circumstances, and an object of the present invention is therefore to
improve the brightness and visibility of white displaying in a
retroreflection-type display device that uses a scattering display mode.

Means for Solving the Problems

[0029]A reflection-type display device according to the present invention
is a reflection-type display device with a plurality of pixel regions,
including: a light modulation layer; a front substrate and a rear
substrate between which the light modulation layer is held; an electrode
structure for varying optical characteristics of the light modulation
layer for each pixel region; a retroreflective layer which is placed on a
rear side of the light modulation layer; and a non-retroreflection member
which is placed on the rear side of the light modulation layer and which
has reflection characteristics different from retroreflection, in which
the front substrate includes a light shielding layer which defines an
opening in the each pixel region, and in which the opening contains a
non-retroreflection region, which is defined by the non-retroreflection
member, and a retroreflection region, which is defined by the
retroreflective layer.

[0030]In a preferred embodiment, when viewed from a normal line direction
of the rear substrate, the non-retroreflection region takes up 1/3 or
less of an entire area of the opening.

[0031]The non-retroreflection region may be disposed at a rim of the
opening.

[0032]The retroreflective layer may be placed across the rear substrate
from the light modulation layer.

[0033]In a preferred embodiment, the non-retroreflection member is
interposed between the retroreflective layer and the light modulation
layer to reflect part of light entering the retroreflective layer from a
viewer side in a direction different from a retroreflection direction.

[0034]In a preferred embodiment, the reflection-type display device
further includes wiring lines which are formed on the rear substrate, and
part of the wiring lines is placed within the opening to function as the
non-retroreflection member.

[0035]In a preferred embodiment, the electrode structure includes: a
counter electrode, which is formed on the front substrate; and pixel
electrodes, which are formed on the rear substrate and spaced apart from
one another for the each pixel region, the pixel electrodes each include:
a reflective metal layer; and a transparent conductive layer, and at
least part of the reflective metal layer is placed within the opening to
function as the non-retroreflection member.

[0036]In a preferred embodiment, the electrode structure includes: a
counter electrode, which is formed on the front substrate; and pixel
electrodes, which are formed on the rear substrate and spaced apart from
one another for the each pixel region, the reflection-type display device
further includes a reflective metal layer, which is placed between the
pixel electrodes and the retroreflective layer, and at least part of the
reflective metal layer is placed within the opening to function as the
non-retroreflection member.

[0037]The wiring lines formed on the rear substrate are preferably
shielded against light by the light shielding layer and the reflective
metal layer.

[0038]The non-retroreflection member preferably includes a substantially
flat non-retroreflection region.

[0039]The non-retroreflection region may be parallel to the rear
substrate.

[0040]Another reflection-type display device according to the present
invention is a reflection-type display device with a plurality of pixel
regions, including: a light modulation layer; a front substrate and a
rear substrate between which the light modulation layer is held; an
electrode structure for varying optical characteristics of the light
modulation layer for each pixel region; and a retroreflective layer which
is placed between the rear substrate and the light modulation layer, and
which has a plurality of unit features arranged two-dimensionally, in
which the front substrate includes a light shielding layer which defines
an opening in the each pixel region, in which the retroreflective layer
includes a plurality of reflection electrodes, which are spaced apart
from one another for the each pixel region. The reflection-type display
device further includes: a plurality of switching elements which are
formed on the rear substrate; and a contact portion which electrically
connects each of the reflection electrodes with its associated switching
element, in which the plurality of reflection electrodes each include,
within the opening: a retroreflection region, which includes the
plurality of unit features; and a substantially flat non-retroreflection
region, and in which the non-retroreflection region is placed above the
contact portion and, when viewed from a normal line direction of the rear
substrate, is larger in area than each unit feature.

EFFECTS OF THE INVENTION

[0041]According to the present invention, the retroreflection-type display
device that uses a scattering display mode may display a bright image at
excellent visibility in any viewing direction by providing the
non-retroreflection region in the opening.

[0042]The width of a light shielding layer formed on the front substrate
may be set narrower than in prior art, and the non-retroreflection region
is placed in a part that would conventionally be shielded by the light
shielding layer. This improves the substantial aperture ratio and
therefore is advantageous.

[0044]FIGS. 2(a) and 2(b) are diagrams illustrating a structure of a
conventional retroreflection-type liquid crystal display device, with
FIG. 2(a) illustrating in plan view a state of wiring lines and
electrodes on a rear substrate of the retroreflection-type liquid crystal
display device and FIG. 2(b) schematically illustrating the
retroreflection-type liquid crystal display device in sectional view
taken along lines II-II' and II'-II'' of FIG. 2(a).

[0045]FIGS. 3(a) and 3(b) are diagrams illustrating a relation between a
viewing direction and brightness of white displaying in the conventional
retroreflection-type liquid crystal display device.

[0046]FIGS. 4(a) and 4(b) are diagrams illustrating a relation between a
viewing direction and brightness of white displaying in a
retroreflection-type liquid crystal display device according to
embodiments of the present invention.

[0047]FIGS. 5(a) and 5(b) are diagrams illustrating a structure of a
retroreflection-type liquid crystal display device according to a first
embodiment of the present invention, with FIG. 5(a) illustrating in plan
view a state of wiring lines and electrodes on a rear substrate of the
retroreflection-type liquid crystal display device and FIG. 5(b)
schematically illustrating the retroreflection-type liquid crystal
display device in sectional view taken along lines V-V' and V'-V'' of
FIG. 5(a).

[0048]FIG. 6 is a plan view illustrating a structure of an opening
according to the first embodiment of the present invention.

[0049]FIGS. 7(a) and 7(b) are diagrams illustrating a structure of a
retroreflection-type liquid crystal display device according to a second
embodiment of the present invention, with FIG. 7(a) illustrating in plan
view a state of wiring lines and electrodes on a rear substrate of the
retroreflection-type liquid crystal display device and FIG. 7(b)
schematically illustrating the retroreflection-type liquid crystal
display device in sectional view taken along lines VII-VII' and
VII'-VII'' of FIG. 7(a).

[0050]FIGS. 8(a) and 8(b) are diagrams illustrating a structure of a
retroreflection-type liquid crystal display device according to a third
embodiment of the present invention, with FIG. 8(a) illustrating in plan
view a state of wiring lines and electrodes on a rear substrate of the
retroreflection-type liquid crystal display device and FIG. 8(b)
schematically illustrating the retroreflection-type liquid crystal
display device in sectional view taken along lines VIII-VIII' and
VIII'-VIII'' of FIG. 8(a).

[0051]FIG. 9 is a schematic sectional view illustrating a
retroreflection-type liquid crystal display device according to a fourth
embodiment of the present invention.

[0052]FIG. 10 is a plan view illustrating a structure of an opening
according to the fourth embodiment of the present invention.

[0077]In preferred embodiments of a reflection-type display device
according to the present invention, a retroreflective layer and a
non-retroreflection member are provided on the rear side of a light
modulation layer, and a non-retroreflection region, which is defined by
the non-retroreflection member, and a retroreflection region, which is
defined by the retroreflective layer, are disposed within an opening in a
pixel region. The term "non-retroreflection member" herein means a member
having reflection characteristics that are not retroreflection (specular
reflection characteristics, diffuse reflection characteristics, or the
like). The "opening" herein refers to a portion that is defined by a
light shielding layer (e.g., black matrix) provided on a front substrate
and that contributes to the displaying of an image.

[0078]Advantages of placing not only a retroreflection plate but also a
non-retroreflection member in an opening are described below with
reference to FIGS. 4(a) and 4(b).

[0079]A display device 200 is a retroreflection-type display device that
is equipped with the non-retroreflection member. Here, a plane mirror
disposed substantially parallel to a substrate surface of the
reflection-type display device is employed as the non-retroreflection
member. For the sake of simplification, components similar to those of
the display device 100 illustrated in FIGS. 3(a) and 3(b) are denoted by
the same reference symbols.

[0080]First, FIG. 4(a) is referred to. In the white displaying state,
light from a light source 5 passes through a light modulation layer 1
within an opening of the display device 200 and enters a retroreflective
layer 2 or the plane mirror (not shown) Light incident on the
retroreflective layer 2 is reflected toward a direction 30 of the light
source 5 (retroreflection direction), and then scattered once more by the
light modulation layer 1 to exit to the viewer side (scattered light La).
The scattered light La has, as described above with reference to the
schematic diagram of FIG. 3(a), an angle distribution centered around the
retroreflection direction 30. On the other hand, light incident on the
plane mirror is reflected in a regular reflection direction 32 by the
plane mirror, and then scattered once more by the light modulation layer
1 to exit to the viewer side (scattered light Lb). The scattered light Lb
has an angle distribution centered around the regular reflection
direction 32 as schematically illustrated in the drawing. As illustrated
in the drawing, when the viewing direction of a viewer 6 is relatively
close to the retroreflection direction 30 and the regular reflection
direction 32, and the scattered light La and the scattered light Lb are
intense enough in the viewing direction, highly intense light Lo, which
contains the scattered light Lb as well as the scattered light La,
contributes to making the displayed image extremely bright.

[0081]The conventional display device 100, too, may display a bright image
owing to the scattered light La when the retroreflection direction 30 and
the viewing direction are relatively close to each other, as has been
described with reference to FIG. 3(a). The display device 200, which
displays utilizing the scattered light Lb that the non-retroreflection
member reflects in addition to the scattered light La, is further
enhanced in brightness of white displaying.

[0082]A case in which the viewing direction of the viewer 6 is
significantly distant from the retroreflection direction 30 is considered
next with reference to FIG. 4(b). As illustrated in the drawing, when the
viewing direction and the retroreflection direction 30 are far from each
other with respect to the normal line direction of substrates 10 and 12,
the light La scattered by the light modulation layer 1 after reflected by
the retroreflective layer 2 does not have sufficient intensity in the
viewing direction. Nevertheless, the displayed image is bright because
the light Lo, which is part of the light Lb scattered by the light
modulation layer 1 after regularly reflected by the plane mirror, exits
toward the viewing direction and contributes to the displaying of an
image. The display device 200 is therefore greatly improved in brightness
of white displaying compared to the conventional display device 100,
which has been described with reference to FIG. 3(b).

[0083]The display device 200 in the white displaying state thus displays
utilizing (1) the scattered light La, which is light traveling through
the light modulation layer 1 within the opening, then reflected by the
retroreflective layer 2 toward the light source direction
(retroreflection direction) 30, and then scattered by the light
modulation layer 1 to exit to the viewer side, and (2) the scattered
light Lb, which is light traveling through the light modulation layer 1
within the opening, then reflected by the non-retroreflection member, and
then scattered by the light modulation layer 1 to exit to the viewer
side, as well. The display device 200 may accordingly display a brighter
image than the conventional display device 100, which utilizes the
scattered light La alone. Also, while the conventional display device 100
has a problem in that the white displaying characteristics are markedly
poor in some viewing directions as described with reference to FIG. 3,
the present invention may expand the angle distribution of light that
contributes to the displaying of an image (i.e., scattered light La and
Lb) and may thus prevent the white displaying characteristics from
deteriorating depending on the viewing direction.

[0084]The non-retroreflection member is not limited to a plane mirror. Any
member that has other reflection characteristics than retroreflection
characteristics enables the display device 200 to utilize the scattered
light Lb, which differs from the scattered light La, in displaying an
image and may therefore improve the brightness of white displaying,
though the exit direction and intensity of the scattered light Lb vary
depending on what reflection characteristics the member has. However, a
non-retroreflection member having a planar surface is preferred because
such a non-retroreflection member hardly causes scattering in the black
displaying state as well and therefore leads to excellent display
quality. The non-retroreflection member more desirably has a planar
surface that is parallel to the surface of the rear substrate 12, and
hence the brightness of white displaying may be improved more effectively
by utilizing for the displaying of an image the scattered light La which
exits in directions centered around the retroreflection direction and the
scattered light Lb which exits in directions centered around the regular
reflection direction as illustrated in FIG. 4.

First Embodiment

[0085]A first embodiment of a display device according to the present
invention is described below with reference to the drawings. The display
device of this embodiment is a retroreflection-type liquid crystal
display device using a scattering-type liquid crystal, and has an
external MCCA structure. A non-retroreflection member in this embodiment
is a reflective metal layer formed from reflective metal such as silver
(Ag), and has a surface containing a plane that exhibits specular
reflection characteristics (plane mirror). A reflective metal layer as
this is provided in each pixel region, and also functions as part of a
pixel electrode.

[0086]FIG. 5(a) is a plan view illustrating a state of wiring lines and
electrodes on a rear substrate of the display device according to this
embodiment. FIG. 5(b) is a diagram illustrating the display device of
this embodiment, specifically, a schematic sectional view taken along
lines V-V' and V'-V'' in the plan view of FIG. 5(a). For the sake of
simplification, components that are the same as those of the display
device 100 are denoted by the same reference symbols and their
descriptions are omitted.

[0087]The display device 200 includes a plurality of pixel electrodes 56
on the same side of the rear substrate 12 as the light modulation layer
1, with a transparent resin layer 22 interposed between the rear
substrate 12 and the pixel electrodes 56. The pixel electrodes 56 each
include a transparent conductive layer 51, which is formed from a
transparent conductive material such as ITO, and a reflective metal layer
(here, Ag layer) 53, which is placed at the rim of the transparent
conductive layer 51 and electrically connected to the transparent
conductive layer 51. The reflective metal layer 53 here is disposed to
hem the transparent conductive layer 51 and to partially cover source
lines 14 and gate lines 15, which are formed on the rear substrate 12.
The pixel electrodes 56 are spaced apart from one another and each define
a pixel region 40, which constitutes one unit of pixel display. A gap 58
between adjoining pixel electrodes 56 is covered with a black matrix 20
formed on the front substrate 10. Each pixel region 40 has substantially
at its center a portion (opening) 50 that is not shielded against light
by the black matrix 20.

[0088]The "pixel region 40" in this embodiment corresponds to a pixel,
which is the smallest unit of displaying an image. The area of each pixel
region 40 is expressed as Px×Py where a pitch between the pixel
electrodes 56 in the row direction is given as Px and a pitch between the
pixel electrodes 56 in the column direction is given as Py.

[0089]In this embodiment, at least part of the reflective metal layer 53
is placed in the opening 50 and functions as a non-retroreflection
member. Specifically, part of light that is about to enter the
retroreflective layer 2 from the viewer side of the display device 200 is
reflected in a direction different from the retroreflection direction
(for example, regular reflection direction).

[0090]FIG. 6 is a plan view illustrating a single opening 50 in the
display device 200 viewed from the normal line direction of the
substrates 10 and 12. As illustrated in the drawing, the opening 50 is a
part that is not covered with the black matrix 20, and includes a
non-retroreflection region 50n, which reflects incident light in a
direction other than the retroreflection direction, and a retroreflection
region 50r, which reflects incident light in the retroreflection
direction. Accordingly, light incident on the opening 50 from the viewer
side is reflected by any one of the non-retroreflection region 50n and
the retroreflection region 50r. In this embodiment, the
non-retroreflection region 5 on is defined by a part of a surface of the
reflective metal layer 53 that is not shielded against light by the black
matrix 20, whereas the retroreflection region 50r is defined by a part of
the retroreflective layer 2 that is not shielded against light neither by
the black matrix 20 nor by the reflective metal layer 53.

[0091]The opening 50 in this embodiment is thus provided with the
non-retroreflection region 50n as well as the retroreflection region 50r.
The displayed image is consequently bright and high in visibility in any
viewing direction as has been described with reference to FIGS. 4(a) and
4(b).

[0092]In the conventional display device 100 described with reference to
FIGS. 2(a) and 2(b), the source lines 14 and the gate lines 15 need to be
placed in a region that is shielded against light by the black matrix 20,
and the width of the black matrix 20 therefore may not be set smaller
than the width of the wiring lines 14 and 15. Further, the black matrix
20 needs to be even wider if gaps from the pixel electrode 16 to the
wiring lines 14 and 15, too, are to be shielded against light, and the
aperture ratio is accordingly lowered. In this embodiment, on the other
hand, the black matrix 20 needs to shield only the gap 58 between
adjoining pixel electrodes 56 against light and may therefore be reduced
in width. The substantial aperture ratio is improved as a result.

[0093]The reflective metal layer 53 is preferably disposed to shield
against light the wiring lines 14 and 15 formed on the rear substrate 12,
except the parts that are shielded against light by the black matrix 20.
In this way, the reflective metal layer 53 and the black matrix 20 almost
completely shield the wiring lines 14 and 15 against light, thereby
avoiding the deterioration of displaying characteristics (black
displaying characteristics, in particular) due to light incident on
surfaces of the wiring lines 14 and 15.

[0094]In the plan view of FIG. 6, a ratio Rn of the area of the
non-retroreflection region Son to the opening 50 and a ratio Rr of the
area of the retroreflection region 50r to the opening 50 may be set
suitably. The ratio Rn of the area of the non-retroreflection region 50n
to the opening 50 is preferably 3% or higher (e.g., 10% or higher)
because, at that ratio, the enhancement in brightness of white displaying
is ensured more firmly and the display contrast ratio is improved. On the
other hand, the ratio Rn of the area of the non-retroreflection region
50n is preferably 50% or lower of the ratio Rr of the area of the
retroreflection region 50r, in other words, the ratio Rn of the
non-retroreflection region 50n to the opening 50 is 1/3 or less. This is
because, when the ratio Rn of the area of the non-retroreflection region
50n exceeds 1/3, a viewer catches with his/her eyes an accidental
reflection on the display monitor of the display device 200 that is
caused by specular reflection by the reflective metal layer 53 and that
lowers the visibility. The ratio Rn of the area of the
non-retroreflection region 50n is more desirably 20% or lower of the
ratio Rr of the area of the retroreflection region 50r, in other words,
the ratio Rn of the area of the non-retroreflection region 50n to the
opening 50 is 1/6 or less. In this way, black displaying that is not as
dark as intended ("dark-state leakage"), or worse, inversion in gray
scale display ("gray scale inversion") is prevented when the display
device 200 is viewed from a direction near the regular reflection
direction of incident light emitted by the light source 5.

[0095]The "ratio Rn of the area of the non-retroreflection region 50n to
the opening 50" and the "ratio Rr of the area of the retroreflection
region 50r to the opening 50" herein rarer to, respectively, the area
ratio of the non-retroreflection region 50n to the area of the opening 50
and the area ratio of the retroreflection region 50r to the area of the
opening 50 that are viewed From the normal line direction of the
substrate surface. In the case where a plurality of non-retroreflection
regions 50n are placed in a single opening 50, the area of the
non-retroreflection region 50n means the total area of those
non-retroreflection regions 50n. The same applies to a case where a
plurality of retroreflection regions 50r are placed in a single opening
50.

[0096]An example of how the reflective metal layer 53 is formed in this
embodiment is described subsequently.

[0097]First, the transparent resin layer 22 is formed on the rear
substrate 12 where thin film transistors 13 and the wiring lines 14 and
15 have been formed. An ITO film is formed by deposition on the
transparent resin layer 22 and patterned to obtain a plurality of
transparent conductive layers 51. Thereafter, a film of reflective metal
(here, Ag film) is formed by deposition on the transparent resin layer 22
and the transparent conductive layers 51 and patterned, to thereby form
the reflective metal layer 53 electrically connected to the relevant
transparent conductive layer 51.

[0098]The formation method for the reflective metal layer 53 is not
limited to the above-mentioned method. For example, the reflective metal
layer 53 may be formed before the transparent conductive layers 51 are
formed, in which case the reflective metal layer 53 is placed below the
transparent conductive layers 51. The material of the reflective metal
layer 53 may not be Ag but an Ag alloy such as AgPd or AgPdCu.

[0099]The arrangement and shapes of the reflective metal layer 53 and the
transparent conductive layers 51 in this embodiment are not limited to
the arrangement and shapes illustrated in the drawings. The reflective
metal layer 53 in this embodiment may function as a non-retroreflection
member and as a pixel electrode when placed between the light modulation
layer 1 and the retroreflective layer 2 and connected electrically to the
relevant transparent conductive layer 51. While part of the reflective
metal layer 53 overlaps with the transparent conductive layer 51 in the
example of the drawings, the entirety of the reflective metal layer 53
may overlap with the transparent conductive layer 51. Alternatively, the
reflective metal layer 53 may be placed such that the reflective metal
layer 53 does not overlap with the transparent conductive layer 51 but is
in contact with an end face of the transparent conductive layer 51.

[0100]The reflective metal layer 53 may have specular reflection
characteristics, diffuse reflection characteristics, or any other
reflection characteristics as long as they are not of retroreflection.
Preferably, of a surface of the reflective metal layer 53, at least a
part that functions as the non-retroreflection region 50n (part that is
located in the opening 50) is a planar surface (plane mirror) having
specular reflection characteristics. More desirably, this planar surface
is disposed substantially parallel to the surfaces of the substrates 10
and 12. In this way, the deterioration of white displaying
characteristics in some viewing directions is lessened more effectively
as has been described with reference to FIGS. 4(a) and 4(b).

[0101]While placing the reflective metal layer 53 in at least part of the
opening 50 is sufficient, arranging the reflective metal layer 53 at the
rim of the transparent conductive layer 51 as described above is
preferred because it raises the substantial aperture ratio compared to
prior art and improves the light utilization efficiency. In that case,
placing the reflective metal layer 53 along at least part of the rim of
the transparent conductive layer 51, for example, on any one of the gate
line 15 and the source line 14, is enough to obtain the effect of
improving the brightness of white displaying. Further, it is sufficient
if the reflective metal layer 53 is placed in at least one of the
openings 50 that constitute the display device 200.

[0102]The display device 200 has an external MCCA structure but the same
effect is obtained when the reflective metal layer 53 is placed between
the retroreflective layer 2 and the light modulation layer 1 in a display
device with an internal MCCA structure in which the retroreflective layer
2 is placed inside a display panel. The reflective metal layer 53 in this
case may be disposed above a contact portion where the retroreflection
shape of the retroreflective layer 2 tends to be lost.

Second Embodiment

[0103]A second embodiment of a display device according to the present
invention is described below with reference to the drawings. The display
device of this embodiment is a retroreflection-type liquid crystal
display device using a scattering-type liquid crystal, and has an
external MCCA structure. In this embodiment, wiring lines formed on a
rear substrate are utilized as a non-retroreflection member.

[0104]FIG. 7(a) is a plan view illustrating a state of the wiring lines
and electrodes on the rear substrate of the display device according to
this embodiment. FIG. 7(b) is a diagram illustrating the display device
of this embodiment, specifically, a schematic sectional view taken along
lines VII-VII' and VII'-VII'' in the plan view of FIG. 7(a). For the sake
of simplification, components that are the same as those of the display
device 100 are denoted by the same reference symbols and their
descriptions are omitted.

[0105]The width of the black matrix 20 in a display device 300 is smaller
than the width of the source line 14 and the gate line 15, and hence the
source line 14, the gate line 15, and the thin film transistor 13 are, at
least partially, not under the black matrix 20 and placed in an opening
70 in an exposed state. The "opening 70" is a part of a pixel region 60
that is not shielded against light by the black matrix 20. In the display
device 300, an end of the pixel electrode 16 and an end of the black
matrix 20 substantially coincide with each other in a direction in which
the layers are laminated, but the black matrix 20 may overlap with part
of the pixel electrode 16. The rest of the structure of the display
device 300 is the same as that of the display device 100 described above
with reference to FIGS. 2(a) and 2(b), and components similar to those of
the display device 100 are denoted by the same reference symbols in order
to omit their descriptions.

[0106]In this embodiment, the wiring lines 14 and 15 and the thin film
transistor 13 formed on the rear substrate 12 are at least partially
disposed in the opening 70 to function as a non-retroreflection member.
Specifically, part of light that is about to enter the retroreflective
layer 2 from the viewer side of the display device 300 is reflected in a
direction different from the retroreflection direction by specular
reflection or diffuse reflection. The brightness in the white displaying
state is thus improved as has been described with reference to FIGS. 4(a)
and 4(b).

[0107]In the conventional display device 100 described with reference to
FIGS. 2(a) and 2(b), the source lines 14 and the gate lines 15 need to be
placed in a region that is shielded against light by the black matrix 20,
and the width of the black matrix 20 therefore may not be set smaller
than the width of the wiring lines 14 and 15. In this embodiment, on the
other hand, the width of the black matrix 20 is smaller than the width of
the wiring lines 14 and 15 and, accordingly, the substantial aperture
ratio is higher than in prior art.

[0108]This embodiment is similar to the above-mentioned first embodiment
in that the opening 70 has a non-retroreflection region 70n and a
retroreflection region 70r. The non-retroreflection region 70n is defined
by a part of surfaces of the source line 14, the thin film transistor 13,
and the gate line 15 that is not shielded against light by the black
matrix 20. The retroreflection region 70r is defined by a part of the
retroreflective layer 2 that is not shielded against light neither by the
black matrix 20 nor by the wiring lines 14 and 15. In the display device
300, the non-retroreflection region 70n is disposed to hem the
retroreflection region 70r.

[0109]A ratio Rn of the non-retroreflection region 70n to the opening 70
and a ratio Rr of the retroreflection region 70r to the opening 70 have
the same preferred ranges as in the first embodiment. In this embodiment,
the ratio Rn of the non-retroreflection region 70n to the opening 70 may
be adjusted by choosing the width of the source lines 14 and the gate
lines 15 and the width of the black matrix 20 appropriately.

[0110]The display device 300 of this embodiment may be manufactured by the
same method as the one employed for the conventional display device 100,
which is illustrated in FIGS. 2(a) and 2(b), except that the black matrix
20 is designed to have a smaller width than the width of the wiring lines
14 and 15. This means no additional manufacture process for forming a
non-retroreflection member, and therefore is advantageous.

[0111]A display device according to this embodiment may have other
structures than the structure of the display device 300. It is sufficient
in a display device of this embodiment if at least part of the wiring
lines 14 and 15 or of the thin film transistor 13 is disposed in the
opening 70. For examples instead of setting the width of the black matrix
20 small, the width of the wiring lines 14 and 15 may be widened along
their entire or partial length, and hence part of the wiring lines 14 and
15 is placed in the opening 70. Also, in the display device 300
illustrated in FIG. 7, the position of the non-retroreflection region 70n
defined by the wiring lines 14 and 15 and the shape of the
non-retroreflection region 70n in plan view are not particularly limited,
and a suitable location and shape may be selected.

[0112]While the display device 300 uses the wiring lines 14 and 15 as a
non-retroreflection member, an auxiliary capacitance line may be used as
a non-retroreflection member in addition to, or instead of, the wiring
lines 14 and 15. An auxiliary capacitance line as such may be disposed,
for example, close to the gate line or may run along the gate and source
lines forming the shape of the letter C.

Third Embodiment

[0113]A third embodiment of a display device according to the present
invention is described below with reference to the drawings. The display
device of this embodiment is a retroreflection-type liquid crystal
display device using a scattering-type liquid crystal, and has an
external MCCA structure. In this embodiment, a reflective metal layer is
provided as a non-retroreflection member between a rear substrate and a
pixel electrode.

[0114]FIG. 8(a) is a plan view illustrating a state of wiring lines and
electrodes on the rear substrate of the display device according to this
embodiment. FIG. 8(b) is a diagram illustrating the display device of
this embodiment, specifically, a schematic sectional view taken along
lines VIII-VIII' and VIII'-VIII'' in the plan view of FIG. 8(a). For the
sake of simplification, components that are the same as those of the
display device 100 are denoted by the same reference symbols and their
descriptions are omitted.

[0115]In a display device 400, a reflective metal layer (Ag layer, for
example) 71 is formed above the source line 14 and/or the gate line 15,
which is formed on the rear substrate 12, with a passivation film
(silicon nitride film, for example) 73 interposed between the reflective
metal layer 71 and the wiring line 14 or 15. The reflective metal layer
71 is covered with the transparent resin layer 22, which electrically
insulates the reflective metal layer 71 from the pixel electrode 16. At
least part of the reflective metal layer 71 is not under the black matrix
20, which is provided on the front substrate 10, and is placed in an
exposed state in an opening 90. The "opening 90" is a part of a pixel
region 80 that is not shielded against light by the black matrix 20. In
the display device 400, an end of the pixel electrode 16 and an end of
the black matrix 20 substantially coincide with each other in a direction
in which the layers are laminated, but the black matrix 20 may overlap
with part of the pixel electrode 16.

[0116]In this embodiment, a part of the reflective metal layer 71 that is
positioned in the opening 90 exerts a function as a non-retroreflection
member by reflecting part of light that is about to enter the
retroreflective layer 2 from the viewer side of the display device 400 in
a direction different from the retroreflection direction (for example,
regular reflection direction). The brightness in the white displaying
state is thus improved as has been described with reference to FIGS. 4(a)
and 4(b).

[0117]In the conventional display device 100 described with reference to
FIGS. 2(a) and 2(b), the source lines 14 and the gate lines 15 need to be
placed in a region that is shielded against light by the black matrix 20,
and the width of the black matrix 20 therefore may not be set smaller
than the width of the wiring lines 14 and 15. In this embodiment, on the
other hand, the black matrix 20 needs to cover only a gap 58 between
adjoining pixel electrodes 16 and may therefore be reduced in width. The
substantial aperture ratio may be improved as a result.

[0118]The width of the reflective metal layer 71 is not particularly
limited, but is preferably set such that the source line 14, the gate
line 15, the thin film transistor 13, and other components formed on the
rear substrate 12 are shielded against light by the reflective metal
layer 71. This prevents the deterioration of displaying characteristics
(black displaying characteristics, in particular) due to light incident
on surfaces of the above-mentioned components.

[0119]This embodiment is similar to the above-mentioned embodiments in
that the opening 90 has a non-retroreflection region 90n and a
retroreflection region 90r. The non-retroreflection region 90n is defined
by a part of the reflective metal layer 71 that is not shielded against
light by the black matrix 20. The retroreflection region 90r is defined
by a part of the retroreflective layer 2 that is not shielded against
light neither by the black matrix 20 nor by the reflective metal layer
71.

[0120]A ratio Rn of the non-retroreflection region 90n to the opening 90
and a ratio Rr of the retroreflection region 90r to the opening 90 have
the same preferred ranges as the ranges described in the first
embodiment. The ratios Rn and Rr may be adjusted by choosing the size of
the reflective metal layer 71 and the width of the black matrix 20
appropriately.

[0121]An example of how the reflective metal layer 71 and the pixel
electrode 16 are formed in this embodiment is described next.

[0122]First, a silicon nitride film is formed by CVD on the rear substrate
12 where the thin film transistor 13 and the wiring lines 14 and 15 have
been formed. The silicon nitride film is patterned to form the
passivation film (thickness: 1,500 angstroms, for example) 73, which
covers the wiring lines 14 and 15 and the thin film transistor 13. Next,
a reflective metal film (Ag film) is vapor-deposited on the passivation
film 73 and then patterned to form the reflective metal layer (thickness:
1, 500 angstroms, for example) 71, which covers the wiring lines 14 and
15 and the thin film transistor 13. A transparent resin material is
applied onto the reflective metal layer 71 by a spin coating technique to
form the transparent resin layer 22. A contact hole that reaches a drain
electrode 13d of the thin film transistor 13 is formed in the transparent
resin layer 22. Thereafter, an ITO film is formed by deposition on the
transparent resin layer 22, and patterned to obtain the pixel electrode
16.

[0123]The formation method for the reflective metal layer 71 is not
limited to the above-mentioned method. The material of the reflective
metal layer 71 may not be Ag but an Ag alloy such as AgPd or AgPdCu.

[0124]The arrangement and shape of the reflective metal layer 71 in this
embodiment are not limited to the arrangement and shape illustrated in
the drawings. The reflective metal layer 71 in this embodiment only needs
to be placed between the pixel electrode 16 and the retroreflective layer
2 in the opening 90. The reflective metal layer 71 may be, for example,
smaller in width than the wiring lines 14 and 15 to an extent that part
of the wiring lines 14 and 15 is not shielded against light by the
reflective metal layer 71. Also, while part of the reflective metal layer
71 in the display device 400 overlaps with the pixel electrode 16, a
narrow reflective metal layer 71 may be formed so that the reflective
metal layer 71 is covered with the pixel electrode 16.

[0125]The reflective metal layer 71 may have specular reflection
characteristics, diffuse reflection characteristics, or any other
reflection characteristics as long as they are not of retroreflection.
Preferably, of a surface of the reflective metal layer 71, at least a
part that functions as the non-retroreflection region 90n (part that is
located in the opening 90) is a planar surface (plane mirror) having
specular reflection characteristics. More desirably, this planar surface
is disposed substantially parallel to the surfaces of the substrates 10
and 12. In this way, the deterioration of white displaying
characteristics in some viewing directions is lessened more effectively
as has been described with reference to FIGS. 4(a) and 4(b).

[0126]Placing the reflective metal layer 71 in at least part of the
opening 90 is sufficient. For example, placing above merely any one of
the gate line 15 and the source line 14 is enough to obtain the effect of
improving the brightness of white displaying. Further, it is sufficient
if the reflective metal layer 71 is placed in at least one of the
openings 90 that constitute the display device 400.

Fourth Embodiment

[0127]A fourth embodiment of a display device according to the present
invention is described below with reference to the drawings. The display
device of this embodiment is a retroreflection-type liquid crystal
display device using a scattering-type liquid crystal, and has an
internal MCCA structure. The display device of this embodiment includes a
reflection electrode, which functions as a pixel electrode and as a
retroreflective layer both, and each opening is provided with a
non-retroreflection region, which is above a contact portion for
connecting the reflection electrode with a thin film transistor.

[0128]FIG. 9 is a schematic sectional view of the display device of this
embodiment.

[0129]A display device 500 includes a front substrate 10, where a color
filter 19, a black matrix 20, and a counter electrode 18 are provided, a
rear substrate 12, which is disposed to face the front substrate 10, and
a light modulation layer 1, which is provided between the substrates 10
and 12. In this embodiment, a scattering-type liquid crystal layer is
used as the light modulation layer 1. A plurality of thin film
transistors 13 and wiring lines (not shown) are formed on the rear
substrate 12. Formed on the thin film transistors 13 and the wiring
lines, in the order stated, are an insulating layer 92, which has a
surface shaped to exhibit retroreflection properties, and a plurality of
reflection electrodes 94.

[0130]The plurality of reflection electrodes 94 are spaced apart from one
another pixel by pixel. Each reflection electrode 94 is connected to a
drain electrode of its associated thin film transistor 13 through a
contact portion 96 formed in the insulating layer 92. Each reflection
electrode 94 has an irregular surface that reflects the surface shape off
the insulating layer 92. In the display device 500, the reflection
electrode 94 exerts a function as a pixel electrode and a function as a
retroreflective layer.

[0131]The reflection electrode 94 here has an MCCA shape and defines a
retroreflection region 120r. However, as illustrated in the drawing, the
surface of a part of the reflection electrode 94 that is above the
contact portion 96 in the opening 120 defines a non-retroreflection
region 120n. The non-retroreflection region 120n contains a substantially
flat region as may be seen in the drawing. The "opening 120" is a part of
a pixel region 110 that is not shielded against light by the black matrix
20.

[0132]FIG. 10 is a plan view illustrating a single opening 120 of the
display device 500 viewed from the normal line direction of the
substrates 10 and 12.

[0133]In the plan view of FIG. 10, the area of the non-retroreflection
region 120n is equal to or larger than the area of a concavo-convex unit
feature in the reflection electrode 94, more desirably, 1.5 times the
area of the unit feature or larger. In this way, the improvement in
brightness of white displaying is ensured more firmly. The "area of the
unit feature" viewed from the normal line direction of the surfaces of
the substrates 10 and 12 is, when the reflection electrode 94 has, for
example, a cubic corner cube array shape as the one illustrated in FIGS.
11(a) and 11(b), the area of a regular hexagon constituted by peak points
and saddle points, or the area of a regular hexagon constituted by bottom
points and saddle points, in a plan view of FIG. 11(b). A ratio Rn of the
non-retroreflection region 120n to the opening 120 has the same preferred
range as the range described in the first embodiment.

[0134]In this embodiment, in which the retroreflection region 120r and the
non-retroreflection region 120n are placed in the opening, part of light
that is about to enter the reflection electrode 94 from the viewer side
of the display device 500 is reflected by the non-retroreflection region
120n in a direction different from the retroreflection direction (for
example, regular reflection direction), and exits to the viewer side. The
brightness in the white displaying state is thus improved as has been
described with reference to FIGS. 4(a) and 4(b).

[0135]JP 2003-255373 A by the applicant of the present invention discloses
findings in which, due to contact portions, reflection electrodes in a
display device having an internal MCCA structure lose their MCCA shape
and are substantially leveled When a contact portion causes a reflection
electrode to lose its MCCA shape and a substantially flat portion is
formed as a result, however, the area of the substantially flat portion
is about 1/2 of the area of the unit feature in the MCCA shape of the
reflection electrode when viewed from the normal line direction of the
substrate, and the white displaying characteristics may not be Improved
enough. This embodiment takes a totally opposite approach and utilizes
the fact that a part of the reflection electrode 94 that is located above
the contact portion 96 loses its retroreflection shape, by proactively
forming a region 120n that does not have retroreflection characteristics
(non-retroreflection region) in a given portion that contains the contact
portion 96. The non-retroreflection region 120n in this embodiment is as
large as the area of the unit feature in the MCCA shape or more, which is
large enough to improve the white displaying characteristics.

[0136]The reflection electrode 94 having the non-retroreflection region
120n as this may be formed by, for example, the following method.

[0137]First, an MCCA having a plurality of convex portions and flat
surfaces surrounding the convex portions Is manufactured as a master.
Next, an insulating layer is formed on the rear substrate 12 where the
thin film transistors 13 and the wiring lines have been formed and, for
example, the shape of the above-mentioned master is transferred to this
insulating layer to obtain the insulating layer 92. A part of the
insulating layer 92 that corresponds to the convex portions of the master
constitutes a contact hole, whereas a part of the insulating layer 92
that is defined by the flat surfaces of the master constitutes the
non-retroreflection region 120n. Subsequently, a metal film is formed by
deposition on the insulating layer 92 and in the contact hole, and then
patterned. As a result, a plurality of reflection electrodes 94 having
the non-retroreflection regions 120n are formed while the contact
portions 96 are formed in contact holes at the same time. The display
device 500 of this embodiment may thus be manufactured without
complicating the conventional manufacture process, and therefore is
advantageous.

[0138]The light modulation layer 1 in the above-mentioned first through
fourth embodiments may be any layer capable of switching between a
transmitting state in which light incident on the light modulation layer
1 passes through the light modulation layer 1 maintaining its traveling
direction (including cases where incident light travels while refracted)
and a scattering state in which the traveling direction is changed by a
scattering effect. For example, the light modulation layer 1 is
constituted by a nematic-cholesteric phase transition type liquid
crystal, a polymer-dispersed type liquid crystal which has a holographic
function or a diffraction function, or a light scattering-type liquid
crystal such as liquid crystal gel.

[0139]Preferably, a polymer-dispersed type liquid crystal is used as a
scattering-type liquid crystal. A polymer-dispersed type liquid crystal
is obtained by, for example, dissolving a mixture of a
low-molecular-weight liquid crystal composition and an unpolymerized
prepolymer in a compatible manner, placing the mixture between the front
substrate 10 and the rear substrate 12 where electrodes and others have
been formed, and then polymerizing the prepolymer. The prepolymer is not
limited to a particular type but, preferably, a UV-curing prepolymer.
When a UV-curing prepolymer is used, the above-mentioned mixture does not
need to be heated in the polymerization, and adverse effects of heat on
other members are thus avoided.

[0140]A polymer-dispersed type liquid crystal as the one described above
may be formed by preparing a mixture (prepolymer/liquid crystal mixture)
of a UV-curing prepolymer that exhibits liquid crystal properties and a
liquid crystal composition (TL 213: a product of Merck, Δn=0.238),
and photo-curing the mixture through irradiation of an active ray such as
a UV ray. The prepolymer/liquid crystal mixture may be, for example, a
prepolymer/liquid crystal mixture exhibiting the nematic liquid crystal
phase at room temperature, which is obtained by mixing a UV-curing
material and a liquid crystal at a weight ratio of 20:80 and adding a
small amount of polymerization Initiator (Irgacure 651: a product of
Nihon Ciba-Geigy K.K.). The above-mentioned polymer-dispersed type liquid
crystal is thus formed through UV-ray irradiation and does not need heat
treatment. This lessens the damage brought by forming the light
modulation layer 1 to other members that are formed on the front
substrate 10 and the rear substrate 12.

[0141]The retroreflective layer 2 in the above-mentioned first through
fourth embodiments may be any reflection plate that has retroreflection
characteristics, but is preferably a corner cube array, more desirably, a
cubic corner cube array as the one illustrated in FIGS. 11(a) and 11(b).
A cubic corner cube array is structured such that corner cubes each of
which is constituted by three substantially square faces orthogonal to
one another are arranged two-dimensionally. Cubic corner cube arrays have
particularly excellent retroreflection characteristics among all types of
corner cube array. The arrangement pitch of cubic corner cubes is
preferably much smaller than the pixel pitch of a display device, for
example, 5 μm or more and 50 μm or less.

[0142]The present invention is widely applicable to reflection-type
display devices that use a scattering display mode and a retroreflection
plate in combination. For example, the present invention is favorably
applied to retroreflection-type liquid crystal display devices that use a
polymer-dispersed type liquid crystal. A display device of this type may
have an internally located structure in which a retroreflection plate is
placed inside the display panel, or an externally located structure in
which a retroreflection plate is placed on the rear side of the display
panel. The present invention more effectively improves the displaying
characteristics of retroreflection-type liquid crystal display devices
having the externally located structure, particularly when a gap between
the retroreflection plate and the rear substrate of the display panel is
filled with a substance that has a refractive index of 1.06 or higher.
Why it is so is described below.

[0143]In the case where the employed retroreflection plate is an MCCA as
the one illustrated in FIGS. 11(a) and 11(b), light 260 enters
perpendicularly to the MCCA as illustrated in the drawing. As illustrated
in FIG. 11(b), the light 260 is reflected sequentially by three faces
constituting a corner cube that the light 260 has entered (incident
corner cube), and becomes retroreflected light that returns to the
incident direction. Light 280, on the other hand, enters at an angle with
respect to the perpendicular direction of the MCCA and, even when the
tilt is as slight as a few degrees, part of the light 280 is reflected
sequentially by two faces out of the three faces that constitute the
incident corner cube as illustrated in FIG. 11(b). The light component
does not enter the remaining face and therefore is not returned to the
incident direction. Light like this which is reflected by only two faces
constituting an incident corner cube is called "twice-reflected light".
Twice-reflected light is generated also when light enters in a direction
perpendicular to the MCCA if the MCCA shape precision (measured by normal
line angle and planarity) is low.

[0144]In a display device where the MCCA is placed on the rear side of the
display panel and a gap between the rear face of the display panel and
the MCCA is filled with a substance having a refractive index of about
1.00 (for example, air), when the display device is in the white
displaying state, part of twice-reflected flight exits to the viewer side
after scattered by a liquid crystal layer, despite the viewer having a
direct view of the display panel. This means that light that is
twice-reflected light scattered by the liquid crystal layer may be
utilized for the displaying of an image as well as light that is
retroreflected light scattered by the liquid crystal layer. On the other
hand, in a display device where a gap between the rear face of the
display panel and the MCCA is filled with a substance having a refractive
index of 1.06 or higher, when the viewer has a direct view of the display
panel, twice-reflected light does not exit to the viewer side and
accordingly may not be utilized for the displaying of an image. In such a
display device, the lowering of the brightness and visibility in white
displaying is more prominent, and applying the present invention improves
the white displaying characteristics more effectively.

EXAMPLES

[0145]Examples 1 and 2 of the display device according to the present
invention were manufactured, and their displaying characteristics were
measured. The method and results are described. For comparison, a
comparative example was manufactured, which had no non-retroreflection
member, and similar measurements were taken.

[0146]As the comparative example, a display device having the same
structure as that of the display device 100 described with reference to
FIGS. 2(a) and 2(b) was manufactured first. The employed manufacturing
method is as follows.

[0147]A glass substrate was used as the rear substrate 12. The thin film
transistors 13, the source lines 14, the gate lines 15, and auxiliary
capacitance lines were formed on the glass substrate. Though not
illustrated in the drawings, the auxiliary capacitance lines were placed
close to the gate lines 15. The source lines 14, the gate lines 15, and
the auxiliary capacitance lines were formed from tantalum, tungsten, and
molybdenum, respectively. A transparent resin material was applied by
spin coating onto the thus obtained TFT substrate, to thereby form the
transparent resin layer (thickness: 1 μm) 22. An ITO film was formed
on the transparent resin layer 22 by deposition, and then patterned to
form the pixel electrodes 16. Meanwhile, a glass substrate was used as
the front substrate 10 to form the color filters 19, the black matrix 20,
and the counter electrode 18 on the glass substrate. The black matrix 20
was disposed to cover the wiring lines (source lines 14, gate lines 15,
and auxiliary capacitance lines) formed on the rear substrate 12.
Thereafter, a surface of the rear substrate 12 on a side where the pixel
electrodes 16 and other elements were formed and a surface of the front
substrate 10 on a side where the counter electrode 18 and other elements
were formed were faced against each other. A polymer-dispersed type
liquid crystal was injected between the substrates to form the light
modulation layer 1. Lastly, a retroreflection plate was matched with and
attached to the rear side of the rear substrate 12 with the use of
glycerin, thereby forming the retroreflective layer 2. The
retroreflection plate employed was a cubic corner cube array having a
20-μm pitch.

[0148]In the obtained display device of the comparative example, a color
filter opening area ratio was 74%. The R, G, and B filters are
individually surrounded by black matrix segments, and the "color filter
opening area ratio" means the area ratio of the filter to a portion
enclosed by the center lines of the black matrix segments which is equal
to the area ratio of an opening to a pixel region. The black matrix 20
completely shields the wiring lines 14 and 15 against light, and there is
no non-retroreflection region in any of the openings. A ratio Rn of the
non-retroreflection region to the opening is therefore 0%.

[0149]A display device of Example 1 has the same structure as that of the
display device 200 described in the first embodiment with reference to
FIGS. 5(a) and 5(b). The method employed to manufacture the display
device of Example 1 is as follows.

[0150]A TFT substrate was fabricated by a method similar to the one
employed in the above-mentioned comparative example. The transparent
resin layer 22 was formed on the TFT substrate. On the transparent resin
layer 22, the transparent conductive layers 51 were formed from an ITO
film. Silver (Ag) was deposited by evaporation on the transparent resin
layer 22 and the transparent conductive layers 51, and then patterned to
form a plane mirror, which served as the reflective metal layer 53. The
plane mirror was disposed to cover the thin film transistors 13 and the
wiring lines 14 and 15 on the TFT substrate. A part of the plane mirror
that is located in the opening 50, namely, the non-retroreflection region
50n, was given a width of 6 μm. In this manner, the pixel electrodes
56 constituted by the transparent conductive layers 51 and the reflective
metal layer 53 were obtained. Meanwhile, the color filters 19, the black
matrix 20, and the counter electrode 18 were formed on the front
substrate 10 by a method similar to the one employed in the comparative
example. In this example, however, the black matrix 20 did not need to
completely shield the wiring lines 14 and 15 against light, and the width
of the black matrix 20 was therefore set smaller than the width of the
black matrix 20 in the comparative example. Next, the same material and
method as in the comparative example were used to form the light
modulation layer 1 between the front substrate 10 and the rear substrate
12. Thereafter, a retroreflection plate was attached to the rear side of
the rear substrate 12 to form the retroreflective layer 2. The display
device was thus completed.

[0151]In the display device of Example 1, the color filter opening area
ratio was 87%, which was higher than the color filter opening area ratio
in the comparative example. This is owing to the reduction in width of
the black matrix 20 of this example from the width of the black matrix 20
in the comparative example. Further, the ratio Rn of the
non-retroreflection region to the opening in Example 1 was 15%.

[0152]A display device of Example 2 has the same structure as that of the
display device 300 described in the second embodiment with reference to
FIG. 7. The method employed to manufacture the display device of Example
2 was the same as the manufacturing method for the display device of the
comparative example, except that the width of the black matrix 20 was set
smaller than the width of the wiring lines 14 and 15. Specifically, in
Example 2, the width of the source lines 14 and the gate lines 15 was set
equal to the width of the source lines 14 and the gate lines 15 in the
comparative example, and the black matrix 20 was set to a width smaller
by 12 μm than the width of those wiring lines 14 and 15. As a result,
the width of a part of the wiring lines 14 and 15 that is located in the
opening 70, namely, the non-retroreflection region 70n, was 6 μm.

[0153]In the display device of Example 2, the color filter opening area
ratio was 87% and the ratio Rn of the non-retroreflection region to the
opening was 15%.

[0154]Described next is how the displaying characteristics of the display
devices of Examples 1 and 2 and the comparative example obtained by the
above-mentioned methods were evaluated.

[0155]For each of these display devices, Y values in the white displaying
state and the black displaying state were measured with the use of a
spectrophotometric colorimeter (CM-1000: a product of Konica Minolta
Sensing, Inc.), and the display contrast ratio was calculated. The Y
value is the reflectance in the XYZ (Yxy) color system, and corresponds
to the "lightness". A specific measurement method is described below.

[0156]First, the display device for measurement was installed In a
spectrophotometric calorimetric system, and Its light modulation layer 1
was set in a scattering state (white displaying state) By using a light
source and an integrating sphere, light was allowed to be incident on the
display device in all directions, and intensity Iw of the light which was
reflected in a direction perpendicular to the substrate of the display
device was measured with a photodetector. The focusing angle of the
photodetector was 10 degrees. On the other hand, as a reference, a
perfectly diffuse plate was installed on this colorimetric system instead
of a display device, and within the light which was reflected by the
perfectly diffuse plate, intensity Ir of the light heading in a direction
perpendicular to the perfectly diffuse plate was measured with the
photodetector. A ratio (Iw/Ir) (%) of the aforementioned light intensity
Iw relative to the light intensity Ir when using the reference was
calculated, and defined as a brightness of white displaying of the
display device.

[0157]Next, after switching the light modulation layer 1 of the display
device into a transmitting state (black displaying state), light was
allowed to be incident on the display device in all directions in a
similar manner to the above, and intensity Ib of the light being
reflected in a direction perpendicular to the substrate of the display
device was measured with the photodetector. A ratio (Ib/Ir) (%) of the
intensity Ib thus obtained relative to the light intensity Ir when using
the reference was calculated, and defined as a brightness of black
displaying.

[0158]Further, from the brightnesses of black displaying and white
displaying obtained in the above-mentioned manner, a display contrast
ratio (Iw/Ib) was determined.

[0159]For each of the display devices, the visibility in the white
displaying state was also evaluated when the viewing direction and a
direction in which light from the light source enters (is reflected by
retroreflection) were relatively close to each other, and when the
viewing direction and the retroreflection direction were significantly
distant from each other in the opposite directions with respect to the
normal line direction of the panel.

[0160]Table 1 indicates results of measuring the brightness of white
displaying and the contrast ratio in the display devices of Examples 1
and 2 and the comparative example. The "white displaying brightness (%)"
in Table 1 is a value calculated in the above-mentioned manner with the
brightness of the perfectly diffuse plate set as 100%.

[0161]The results indicated in Table 1 reveal that brighter white
displaying than in the comparative example is obtained in both of
Examples 1 and 2 which are provided with a non-retroreflection member
according to the present invention. While the comparative example
completely shields a wiring line part in the pixel region against light
with the black matrix 20, Examples 1 and 2 place a non-retroreflection
region in this wiring line part, thereby substantially raising the
aperture ratio and enhancing the intensity (intensity of the
above-mentioned reflected light) Ib of light that contributes to the
displaying of an image. In Example 1, the displayed image was even
brighter than in Example 2. This is because, though those examples have
the same area ratio of the non-retroreflection region, Example 1 uses a
plane mirror of silver high in reflectance as a non-retroreflection
member and thus enhances the intensity Ib of the reflected light even
more, whereas Example 2 uses the top Laces of the wiring lines 14 and 15
as a non-retroreflection member.

[0162]In Example 1, black displaying, too, is brighter than in the
comparative example. However, Example 1 is greatly improved in brightness
of white displaying, and hence a high contrast ratio is obtained in the
end. Black displaying is better in Example 1 than in Example 2, because
the display device of Example 1 covers the thin film transistor 13,
which, having a complicated structure, causes scattering, with a plane
mirror.

[0163]In Example 2, white displaying brighter than in The comparative
example is accomplished but the display contrast ratio is low because of
extremely bright black displaying. However, the display contrast ratio
may be improved to a level equal to that of the comparative example or
higher by optimizing the reflectance of wiring line metal or reducing
scattering at the wiring line edges.

[0164]Visibility evaluation results are described next.

[0165]In the display devices of Examples 1 and 2, the visibility was
higher than in the display device of the comparative example irrespective
of in what environment the display devices are set up. The visibility of
the display devices of Examples 1 and 2 was far superior to the
visibility of the display device of the comparative example particularly
when the viewing direction and the light source direction with respect to
the panel are significantly distant from each other. As has been
described with reference to FIG. 3 and FIG. 4, in the display devices of
Examples 1 and 2, the scattered light Lb which is scattered after
reflected by a non-retroreflection member contributes to the displaying
of an image in addition to the scattered light La which is centered
around the retroreflection direction, with the result that the displayed
image is bright even when viewed from a direction that is difficult for
the scattered light La to reach In this manner, the deterioration of
white displaying characteristics in some viewing directions is lessened
considerably, which is enough to compensate for the slight deterioration
of black displaying characteristics due to the non-retroreflection
region, and the visibility is ultimately enhanced.

[0166]The environment (e.g., relation between the light source direction
and the viewing direction) in which the display devices are set up was
varied more diversely. As a result, it was found that the display device
of Example 1 is superior in visibility to the display device of Example 2
under all the environments. The probable reason is that the
aforementioned fact that the display device of Example 1 is superior in
white displaying characteristics and black displaying characteristics
both to the display device of Example 2 enables the display device of
Example 1 to display a high visibility image irrespective of the light
source location and the viewing point.

INDUSTRIAL APPLICABILITY

[0167]The present invention is widely applicable to the reflection-type
display devices that use the scattering display mode and the
retroreflection plate in combination. For example, the present invention
is favorably applied to the retroreflection-type liquid crystal display
devices that use the polymer-dispersed type liquid crystal. Of such
display devices, in particular, it is possible to more effectively
improve the displaying characteristics by applying the present invention
to retroreflection-type liquid crystal display devices having an
externally located structure in which a gap between the retroreflection
plate and the rear side of the display pane is filled with a substance
that has a refractive index of 1.06 or higher, and retroreflection-type
liquid crystal display devices having an internally located structure in
which the retroreflection plate is placed inside the display panel.